Flexible borehole liners are installed by the eversion process to seal the borehole against flow into or out of the borehole, which flow can cause the spread of ground water contamination. Helpful and general background regarding the utility and function of everting flexible borehole liners is provided by my previously issued U.S. Pat. Nos. 6,910,374 and 7,281,422, the entire disclosures both of which are incorporated herein by reference. The basic installation method propagates an everting borehole liner into the borehole by adding water to the interior of the everting liner, which dilates the liner and causes the liner to displace the borehole fluids (usually water or air) into the formation as the liner is everted into the borehole. In this basic method, the liner installation rate is controlled by the driving pressure of the water added to the interior of the liner, and by the transmissivity of the media surrounding the borehole, which controls the rate that the borehole water can be displaced into that media.
As the liner propagates by eversion, it sequentially seals each flow path which intersects the borehole, such as a fracture, until all the major fractures have been sealed. As the flow paths are sealed, the liner installation rate decreases until it is propagating very slowly. Further installation of the liner to the bottom of the borehole is not practical because of the slow rate of descent. The typical installation time is at least one to two hours until the liner has nearly stopped, and the removal of the liner by inversion requires a similar time.
The drilling of deep boreholes, for whatever purpose the hole is to be used, often requires more than one day's drilling. A flexible liner is an attractive device to seal a borehole at the end of each day during the drilling process to prevent contaminant migration overnight. However, the liner installation and removal process, as commonly performed, requires far too much time and prolongs the drilling of the borehole. Another major disadvantage of previous liner installation methods is that the contaminated borehole water is forced into the surrounding subsurface formation, where it is absorbed into the pore space of the formation and may contaminate otherwise uncontaminated aquifers. Further, the use of a tube to remove the water from beneath the liner as it is emplaced violates the seal of the liner. Removal of the tube causes the subsequent liner removal by eversion to require several days.